French patent applications FR-A-2 749 489 and FR-A-2 749 490 disclose brushes that have non-rectilinear cores, e.g. that are shaped to match the curve of the eye. Such brushes can be unsuitable for some users, since the curve of the brush sometimes requires the user to perform strokes that certain people find difficult.
Patent application EP-A2-1 236 420 discloses a brush having a core that is curvilinear over at least a fraction of its length, the free end of the brush not being in alignment with the axis of the stem. During manufacture and/or use of this brush with a receptacle containing a composition, such a brush sometimes can be relatively difficult to insert into, and/or remove from, the neck of the receptacle.
European patent application EP-A-1 424 024 discloses an applicator comprising a brush having a core that includes a portion carrying the bristles, wherein the longitudinal axis of the portion of the core carrying the bristles forms a non-zero angle of less than 20° with the longitudinal axis of the distal portion of the stem.
Such a brush sometimes requires the user to adapt brush strokes that are used, since the brush sometimes does not enable the user to comb the eyelashes or the eyebrows in the same manner as with a conventional brush that has a core that does not slope relative to the longitudinal axis of the stem.
U.S. Pat. No. 5,853,011 discloses a mascara brush including a cutback portion having a width that varies along the brush. The cutback portion may have a single maximum width.
French patent application FR-A-2 811 525 discloses off-center brushes, some having a core that extends in alignment with the stem and along the longitudinal axis of the stem, the brush having faces that form a non-zero angle with the longitudinal axis of the core. The longitudinal axis of the core and the longitudinal axis of the envelope surface of the brush are generally non-coplanar given the slope of the faces.
A potential drawback of the off-center brushes of FR-A-2 811 525 is that these brushes have an external appearance that sometimes can be disconcerting to the user. In addition, these brushes sometimes are not wiped symmetrically from one end of the brush to the other, thereby causing flattening over continued use.
Brushes are also known that have envelope surfaces with cross-sections that are off-center relative to a core, and that have faces or ridges that all extend substantially parallel to the core.
The bristles of such brushes are implanted in a conventional manner, wherein the faces are cut parallel to the core. Therefore, in such brushes, the longitudinal axis of the envelope surface is parallel (albeit off-center) to the longitudinal axis of the core. Having this shape does not make these envelope surfaces easy to use, nor does having this shape make it possible to obtain desired effects in making up and in engaging eyelashes or eyebrows to lengthen, separate, and curl them. For example, it is often difficult to apply makeup to, and/or comb, eyelashes or eyebrows situated towards the sides of the eye, with the portion of the envelope surface that is widest along the core.